City looks at turning wastewater into drinking water

San Diego is moving forward on a plan to convert wastewater into drinking water in coming years, according to a plan approved unanimously by the City Council’s Natural Resources and Culture Committee Wednesday.

The plan, due in 90 days, would develop a timeline for building a water purification system and spell out the next steps in that process. It would include an analysis of costs, details on how those costs would be split between water and wastewater, and a description of how the project would be built.

Five years ago the city embarked on an $11.8 million demonstration project to see if it could treat wastewater to drinking level standards.

The project uses a multi-stage process of microfiltration and ultrafiltration, followed by reverse osmosis, ultraviolet light and hydrogen peroxide treatment to purify the water.

After 9,000 individual water quality lab tests, the demonstration project found that the purified water met all federal and state drinking water standards. In fact, the treated water contained fewer organic contaminants and dissolved salts than either aqueduct water or drinking water, a staff report stated.

The next stage would be to build an approximately $370 million facility that could produce up to 15 million gallons per day of treated water, supplying about eight percent of the city’s water use. That water would be piped into San Vicente Reservoir, where it would be treated again before being distributed to water users.

The committee also directed staff to look at options for piping the water directly to consumers.

The total cost of purified water would likely be about $2,000 per acre foot – the amount needed to cover an acre a foot deep, city documents stated. That’s costlier than water purchased from Metropolitan Water District, which totals about $1,000 per acre-foot, according to the San Diego County Water Authority.

But by diverting water from its wastewater system, the purification plant could lead to savings that would bring the net cost to about $1,000 per acre-foot. The water could also provide a hedge against drought shortages, officials said.